Swine Flu Sufferers Pass Bug to at Least Two Others, Study Says

Source: bloomberg.com

By Jason Gale

July 24 (Bloomberg) -- Swine flu sufferers pass the bug to about two other people, fostering its spread, according to the first published study of the pandemic strain’s infectiousness in the Southern Hemisphere.

Researchers in New Zealand and the Netherlands used mathematical modeling to estimate the transmission potential of the new H1N1 strain, also known as swine flu. In New Zealand, where winter weather is fanning the worst flu season in more than a decade, the virus may be spreading more easily than it did in Mexico, where it emerged more than four months ago.

The research, published in today’s New Zealand Medical Journal, may help public health officials in North America and Europe anticipate what to expect when the pandemic virus circulates there next winter. The reproduction number in New Zealand is 1.96, meaning that up to 79 percent of people could potentially catch the germ during the epidemic, said Michael Baker, one of the study’s authors.

“To date we have tended to use a lower estimate of 1.5 which was published early in the pandemic based on data from Mexico,” Baker, who is an associate professor of public health at University of Otago in Wellington, said in a statement.

Published estimates of the reproduction number have ranged from 1.4 to 1.6 in Mexico, and 2.0 to 2.6 in Japan. New Zealand has a higher reproduction number than Mexico, possibly because of the winter season and large clusters of cases in certain settings, the authors said.

Winter Bug

England is suffering the worst bout of flu in a decade and the number of swine flu cases in the U.K. rose by 100,000 in the past week, Britain’s Chief Medical Officer Liam Donaldson said yesterday.

The pandemic bug appears to be as contagious as seasonal influenza, and is spreading faster among people aged 10 to 45 years, according to the World Health Organization. The severity of the disease ranges from mild symptoms such as sore throat and muscle ache to severe illnesses including pneumonia that can result in death, WHO said.

Further studies are needed to produce more robust reproduction estimates for New Zealand, the authors said. Effective public health interventions, including improved hygiene-related behavior, could stem the spread of the disease, said co-author Nick Wilson.

“Staying away from work and school while ill and practicing good cough etiquette can all help to lower the spread of this new virus in New Zealand,” Wilson said in the statement.

Even though the estimated reproduction number is higher than that of the Spanish influenza pandemic of 1918, the mortality rate is much lower, the authors said. The Spanish flu pandemic killed more than 40 million people worldwide.

Mortality rates in developed countries from the current pandemic could be as low as one death out of 10,000 cases, Baker and Wilson said in a separate study earlier this month.

To contact the reporter on this story: Jason Gale in Singapore at j.gale@bloomberg.net.

Last Updated: July 24, 2009 02:46 EDT